1. Field of the Invention
The present invention relates to a subscriber authentication suitable for a so called roaming service in a telecommunication in which a mobile subscriber can receive services from a plurality of service providers, each of which having its own mobile telecommunication network.
2. Description of the Background Art
A known mobile telecommunication system has a typical configuration as shown in FIG. 1, which comprises: a first mobile telecommunication network (first network) 10 for a mobile telecommunication service provided by a first service provider, havlng a base station or switching center 11 and a service area 12; a second mobile telecommunication network (second network) 20 for a mobile telecommunication service provided by a second service provider, having a base station or switching center 21 and a service area 22; a mobile subscriber 30 who is basically a subscribed user of the first service provider, but also capable of receiving the roaming service from the second service provider as well; and an on-line communication line 40 for connecting the first network 10 and the second network 20.
In such a mobile telecommunication system, each of the first and second networks 10 and 20 constantly transmits a broadcast information for identifying itself within its own service area, so that the mobile subscriber 30 can recognize which network's service area it is currently located as well as an occurrence of a zone transition from a service area of one network to a service area of another network, by receiving this broadcast information regularly.
Now, in the currently practiced mobile telecommunication services, the aforementioned roaming service, in which the mobile subscriber 30 can receive services from a plurality of service providers such as the first and second service providers of the above example where each service provider has its own mobile telecommunication network such as the first and second networks 10 and 20, has not yet been established, so that there is no prior art for the subscriber authentication for the roaming service.
However, when the conventionally known subscriber authentication procedure used in the conventional automobile telephone service is straightforwardly applied to a case of the roaming service in the mobile telecommunicatlon system of FIG. 1, the resulting subscriber authentication procedure can be expressed by the diagram of FIG. 2, as follows.
Namely, when the mobile subscriber 30 recognizes the occurrence of the zone transition from the first network 10 to the second network 20 according to the received broadcast information, the mobile subscriber 30 transmits its own mobile station Identifier [ID] to the second network 20 at a process (1). This mobile station identifier [ID] is a unique Identification number assigned in advance to the mobile subscriber 30 by the flrst service provider, and the second network 20 registers the mobile station identlfiers of those mobile subscribers of the first network 10 who are capable of receiving the roaming service from the second network 20, which are informed from the first network 10 in advance.
Then, the second network 20 receiving this transmitted moblle station identifier [ID] from the mobile subscriber 30 checks whether this mobile subscriber 30 is one of the subscribers capable of receiving the roaming service from the second network 20 or not, according to the preregistered mobile statlon identifiers.
When the mobile subscriber 30 is Judged as capable of receiving the roaming service from the second network 20, the second network 20 transmits the received mobile station identifier [ID] to the first network 10 via the on-line communication line 40 at the process (2).
When the first network 10 receives the mobile station identifier [ID] from the second network 20, the first network 10 returns an authentication key [K13] assigned and given to the mobile subscriber 30 by the fist service provlder in advance, through the on-line communication line 40 at the process (3).
Then, the second network 20 stores this authentication key [K13], while generating a random number to be used for the authentication, and transmits the generated random number [rnd] as an authentication request to the mobile subscriber 30 at the process (4).
In response, the mobile subscriber 30 enciphers the received random number [rnd] by using the authentication key [K13] given by the first service provlder in advance, and transmits the enciphered random number [K13(rnd)] as an authentication response to the second network 20 at the process (5).
When the second network 20 receives this authentication response from the mobile subscriber 30, the second network 20 deciphers this authentication response by using the stored authentication key [K13] to recover the random number enciphered by the mobile subscriber 30, and verifies the coincidence of the recovered random number and the originally transmitted random number [rnd]. When this coincidence can be verified successfully, the mobile subscriber 30 is authenticated as the true mobile subscriber of the first service provider which is also capable of receiving the roaming service from the second network 20 at the process (6), which completes the initial authentication of the mobile subscriber 30.
After this initial authentication, the second network 20 memorizes the correspondence between the mobile station identifier [ID] and the authentication key [K13], so that the subsequent authentication such as that required at a time of each call set up request from the mobile subscriber 30 can be carried out in a simplified procedure including a transmission of a new random number [rnd'] from the second network 20 to the mobile subscriber 30 at the process (7), a transmission of an enciphered new random number [K13(rnd')] from the mobile subscriber 30 to the second network 20 at the process (8), and the verification of a deciphered new random number at the second network 20 at the process (9).
However, in such a subscriber authentication procedure, the authentication key, which should essentially be kept in secret between the mobile subscriber 30 and the first service provider, must be disclosed to the totally independent second service provider, so that there is a problem concerning the security for the secrecy of the authentication key.